The present invention relates to a method of manufacturing a valve element adapted to be used in a solenoid valve, the valve element having a disk-shaped leaf spring carrying a movable core fitted thereto.
Control valves for controlling the flow of fluid include flow rate control valves, direction control valves and pressure control valves. The flow rate control valve is designed to modify the flow rate of fluid by providing appropriate resistance to the flow by means of a valve element and the direction control valve is designed to allow or block a flow of fluid in a given direction to shift the direction of a flow of fluid also by means of a valve element, whereas the pressure control valve is adapted to regulate the pressure of the flow of fluid in a fluid circuit by means of a valve element. A solenoid valve is a kind of control valve having a valve element to be operated by means of a solenoid.
Known solenoid valves for controlling the flow rate of fluid flowing through a flow path include the one proposed in Japanese Patent Application Laid-Open No. 7-145873. The proposed method of manufacturing refers to a solenoid valve comprising a valve housing having two ports and a valve element fitted to the valve housing, the valve element having a valve seal adapted to take an open position for opening a valve seat and allowing the two ports to communicate with each other or take a closed position for closing the valve seat and blocking the communication therebetween.
A solenoid coil is arranged in the valve housing in order to operate the valve element. A fixed core (fixed iron core) and a movable core (movable iron core) are arranged at the center of the coil so that the valve element may be opened and closed by means of the movable core. As valve elements capable of being operated by a movable core, there has been developed a valve element provided with such movable core fitted thereto. The valve element of this type typically comprises a disk-shaped leaf spring, an outer peripheral seal arranged at the outer periphery of the leaf spring, a movable core with a cup-shaped cross section arranged in a central area of the leaf spring and a valve seal arranged at an end face of the movable core in order to open and close the valve seat.
The inventors of the present invention have studied valve bodies having a movable core fitted thereto as well as methods for manufacturing such a valve element. As a result of intensive research efforts, the inventor of the present invention invented a method of placing a leaf spring in a metal mold with a movable core held in engagement with the central hole of the leaf spring and forming a leaf spring holding section for rigidly holding the movable core and the leaf spring through vulcanization and molding at the time of forming a valve seal for an end wall section of the movable also through vulcanization and molding so that the leaf spring and the movable core may be rigidly held together by the leaf spring holding section formed integrally with the valve seal.
However, the sealing effect of a valve element relative to a valve seat may be ensured when costly fluorine rubber is only used for the valve seal but the arrangement of rigidly holding the movable core in position by means of a fluorine rubber valve seal and preparing the valve seal and the outer peripheral seal simultaneously by molding requires the valve seal to have a large capacity. Then, such a valve seal can be prepared only by using a large volume of costly and heavy fluorine rubber to consequently raise the weight of the valve element and counter all the efforts for reducing the weight of the valve element. Additionally, any attempt for rigidly holding a movable core and a leaf spring together by means of a leaf spring holding section made of expensive fluorine rubber is accompanied by an insufficient holding strength particularly when the leaf spring holding section is poorly contractible during the molding process. Then, the valve element would not be able to enjoy a long service life and the solenoid valve comprising such a valve element would lose reliability.
Therefore, an object of the present invention is to provide a method of manufacturing a highly reliable valve element that can be prepared with a reduced volume of costly fluorine rubber and hence at reduced cost.
Another object of the invention is to provide a method of manufacturing a lightweight valve element.
Still another object of the invention is to provide a method of manufacturing a highly durable valve element wherein the leaf spring and the movable core are rigidly held together with an enhanced level of strength.
According to another aspect of the invention, there is provided a method of manufacturing a valve element adapted to be arranged in a solenoid valve to open and close a valve seat, comprising a step of preparing a leaf spring including an outer peripheral ring section, a hub section having a central hole, and a plurality of radial arm sections for connecting between said outer peripheral ring section and said hub section, a step of forming a ring-shaped outer peripheral seal by vulcanizing and molding an elastic material such as rubber along said outer peripheral ring section, a step of preparing a movable core having a cup-shaped cross-section and including a cylindrical section and an end wall section, said end wall section being arranged at an end of the cylindrical section and having a central through hole, said cylindrical section having on its outer periphery a stepped section to be held in contact with said leaf spring and having a groove section, a step of forming a valve seal through vulcanization and molding at said end wall, said valve seal having a main body section disposed on an outer surface of said end wall section, a small diameter section disposed in said through hole, and an holding section located on an inner surface of said end wall section and connected to said main body section by way of the small diameter section, a step of placing said movable core and said leaf spring in a thermal caulking metal mold and aligning and holding said leaf spring and said stepped section in contact with each other, a step of aligning a holder ring along an outer periphery of said movable core and a step of bringing said holder ring into engagement with said groove by thermal caulking to that said leaf spring and said movable core are rigidly secured to each other by means of said holder ring.